Method and system for device discovery in a wireless video area network

ABSTRACT

A method and system for device discovery in a wireless network is provided. The device discovery involves directionally transmitting a data unit from a transmitting station over a channel in different directions to emulate omni-directional transmission, receiving the data unit transmissions from different directions at a receiving station, determining the quality of the transmissions received from the different directions, and detecting location information for the transmitting station relative to the receiving station based on the highest quality transmission among the transmissions received from the different directions. Further, if a channel has sufficient bandwidth to satisfy direct link communication between two stations, then during a direct link set-up stage, the two stations conduct a probing message exchange using omni-direction transmission, and upon successful probing, obtain communication link status information and set proper communication configurations for the two stations based on the communication link status information.

RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/801,766, filed on May 18, 2006, incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to device discovery in networks, and inparticular to device discovery for a wireless video area network (WVAN).

BACKGROUND OF THE INVENTION

With the proliferation of high quality video, an increasing number ofelectronics devices (e.g., consumer electronics devices) utilize highdefinition (HD) video which can require multiple gigabit per second(Gbps) in bandwidth for transmission. As such, when transmitting such HDvideo between devices, conventional transmission approaches compress theHD video to a fraction of its size to lower the required transmissionbandwidth. The compressed video is then decompressed for consumption.However, with each compression and subsequent decompression of the videodata, some data can be lost and the picture quality can be reduced.

The High-Definition Multimedia Interface (HDMI) specification allowstransfer of uncompressed HD signals between devices via a cable. Whileconsumer electronics makers are beginning to offer HDMI-compatibleequipment, there is not yet a suitable wireless (e.g., radio frequency)technology that is capable of transmitting uncompressed HD videosignals.

The OSI standard provides a seven-layered hierarchy between an end userand a physical device through which different systems can communicate.Each layer is responsible for different tasks, and the OSI standardspecifies the interaction between layers, as well as between devicescomplying with the standard. The OSI standard includes a physical layer,a data link layer, a network layer, a transport layer, a session layer,a presentation layer and an application layer. The IEEE 802 standardprovides a three-layered architecture for local networks thatapproximate the physical layer and the data link layer of the OSIstandard. The three-layered architecture in the IEEE 802 standard 200includes a physical (PHY) layer, a media access control (MAC) layer, anda logical link control (LLC) layer. The PHY layer operates as that inthe OSI standard. The MAC and LLC layers share the functions of the datalink layer in the OSI standard. The LLC layer places data into framesthat can be communicated at the PHY layer, and the MAC layer managescommunication over the data link, sending data frames and receivingacknowledgement (ACK) frames. Together the MAC and LLC layers areresponsible for error checking as well as retransmission of frames thatare not received and acknowledged.

Wireless personal area networks (WPANs) as defined by the IEEE 802standard and similar technologies can suffer interference issues whenseveral devices are connected which do not have enough bandwidth tocarry the uncompressed HD signal, and do not provide an air interface totransmit uncompressed video over a 60 GHz band. The IEEE 802.15.3specifies channel access methods for transmission of audio/visualinformation over WPANs. However, in IEEE 802.15.3, channel accesscontrol is complicated and is only for access to a single channel. Itdoes not allow efficient device discovery in a wireless network, norestablishing direct communication link based on device discovery.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method and system for device discoveryin a wireless network. In one embodiment, device discovery involvesdirectionally transmitting a data unit from a transmitting station overa channel in different directions to emulate omni-directionaltransmission, receiving the data unit transmissions from differentdirections at a receiving station, determining the quality of thetransmissions received from the different directions, and detectinglocation information for the transmitting station relative to thereceiving station, based on the highest quality transmission among thetransmissions received from the different directions.

In another embodiment, the present invention provides a direct linkwireless data communication process, which includes: receiving a requestfor wireless communication between two wireless stations over a wirelesschannel; determining if the channel has sufficient bandwidth to satisfythe communication request; if the channel has sufficient bandwidth tosatisfy the communication request, establishing a direct communicationlink between the two stations over the channel. The step of establishingthe direct communication link, including the steps of: during a directlink set-up stage, the two stations conduct a probing message exchangeusing omni-direction transmission; and upon successful probing,obtaining communication link status information and setting propercommunication configurations for the two stations based on thecommunication link status information.

These and other features, aspects and advantages of the presentinvention will become understood with reference to the followingdescription, appended claims and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a functional block diagram of a wireless network thatimplements uncompressed HD video transmission between wireless stations,according to an embodiment of the present invention.

FIG. 2 shows an example device discovery process, according to thepresent invention.

FIG. 3 shows an example of different direction sections for emulatingomni-directional transmission, according to the present invention.

FIG. 4 shows an example of location detection process, according to thepresent invention.

FIG. 5 shows an example timing diagram for Time Division Duplex (TDD)scheduling applied to low-rate and high-rate wireless communicationchannels in FIG. 1.

FIG. 6A shows example superframe structures for channel access control,according to the present invention.

FIG. 6B shows example details of a superframe structure, according tothe present invention.

FIG. 7 shows an example of a management entity for direct linktransmission in a WVAN, according to the present invention.

FIG. 8 shows an example of direct link set-up procedure in a WVAN,according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and system for device discoveryin a wireless video area network (WVAN) such as a wireless highdefinition (WiHD) WVAN including wireless devices. For device discovery,the same data is directionally transmitted by a transmitter over achannel in different directions to emulate omni-directionaltransmission. One or more receivers utilize the quality of the signalreceived from those different directions to detect the location of thetransmitter. The receivers obtain the location information and updatetheir location information by analyzing periodically received beacons.The location information can be used for direct link support andreduction of the PHY preamble length in the PHY header and the PHYpayload size.

FIG. 1 shows a functional block diagram of a wireless network 10 thatincludes wireless communication stations 12 and 14 implementinguncompressed HD video communication, according to an embodiment of thepresent invention. The wireless communication stations 12 comprise acoordinator 12 such as a WiHD coordinator. The wireless communicationdevices 14 include devices 4 (e.g., Dev-1, . . . , Dev-n). Thecoordinator 12 and the devices 14 utilize a low-rate (LR) channel 16(shown by dashed lines in FIG. 1) and a high-rate (HR) channel 18 (shownby heavy solid lines in FIG. 1) for communication therebetween.

In this embodiment, the coordinator 12 is a sink of video and/or audiodata implemented, for example, in a HDTV set in a home wireless networkenvironment which is a type of WLAN. Each device 14 comprises a devicethat can be the source of uncompressed video or audio. Examples of eachdevice 14 can be a set-top box, a DVD player, etc. A device 14 can alsobe an audio sink. In another example, the coordinator 12 can be a sourceof a video stream. In yet another example, the coordinator provideschannel coordination functions for wireless communication between a sinkstation and a source station. The coordinator functions such as channelaccess functions, according to the present invention can also beimplemented in a stand-alone device, in a sink device and/or in a sourcedevice. A device can be the source of uncompressed video or audio likeset-top box or DVD player. A device can also be an audio sink.

In order to establish a WVAN for communication, available channelfrequencies are scanned to determine available channels (i.e., not inuse by neighboring networks). All LR channels are scanned to findchannels with minimal interference with other networks. Then, thefrequency band of the HR channels is scanned for interference, and achannel with minimal interference is selected.

A total of j channels in the frequency range of 57-66 GHz are defined bya High-Rate Plan (HRP) for the HR frequency. Due to regulatoryrestrictions, not all of these channels are available in all geographicregions. For example, when j=4, four channels are indexed by a HRPchannel index. These HRP frequency channels are defined by example inTable 1 below.

TABLE 1 HRP frequency plan HRP Start Center Stop channel frequencyfrequency frequency index (GHz) (GHz) (GHz) 1 57.2 58.2 59.2 2 59.4 60.461.4 3 61.6 62.6 63.6 4 63.8 64.8 65.8

Each HRP channel has a start frequency, a center frequency and a stopfrequency. The start and stop frequencies define a HRP frequencychannel.

A Low-Rate-PHY frequency Plan for the LRP uses the same frequency bandsas the HRP, wherein within each of the HRP channels, a number k of LRPchannels are defined. In this example, for k=3, three LR channels aredefined for each of the four HRP bands. Only one LRP channel is used bya WVAN at a time. This allows multiple WVANs to use the same HRPfrequency channel in close proximity, while minimizing channelinterference. Each LRP channel is defined relative to the centerfrequency of the corresponding HRP channel, fc(HRP). As such, withineach of the HRP channels, three LRP channels are defined near the centerfrequency of the HRP channel. The LRP frequency channels, indexed by aLRP channel index, are defined by example in Table 2 below.

TABLE 2 LRP frequency plan LRP Start Center Stop channel frequencyfrequency frequency index (GHz) (GHz) (GHz) 1 fc(HRP) − 240 MHz fc(HRP)− 200 MHz fc(HRP) − 160 MHz 2 fc(HRP) − 40 MHz  fc(HRP) fc(HRP) + 40MHz  3 fc(HRP) + 160 MHz fc(HRP) + 200 MHz fc(HRP) + 240 MHz

Each LRP channel has a start frequency, a center frequency and a stopfrequency. The start and stop frequencies define a LRP frequencychannel. In this example, each LRP frequency band is an 80 MHz band, theLRP channels are separated by 120 MHz bands, and the center frequenciesof the LRP channels are separated by 200 MHz bands.

The LRP channel implements orthogonal frequency division multiplexing(OFDM) and offers both omni-directional and beam-steered (i.e.,directional) modes. Directional transmission in different directionsaccording to the present invention comprises beam steered transmissionin different directions. The transmission data rates for the LRP rangefrom 2.5 Mb/s to 10 Mb/s for the omni-directional mode and 20 Mb/s to 40Mb/s for the beam-steered mode. Channel coding includes ⅓, ½ and ⅔convolutional coding. For the omni-directional mode, coding includes4-times (i.e., 4×) or 8-times (i.e., 8×) replication coding, while forthe beam-steered mode there is no replication. A summary of the LRPmodes is provided by example in Table 3 below in indexed form.

TABLE 3 Summary of LRP modes PHY data rate (Mb/s) Replication LRP modebeam beam index Modulation FEC omni formed omni formed 0 BPSK 1/3 2.51220.096 8× 1× 1 1/2 3.768 30.144 8× 1× 2 2/3 5.024 (also 40.192 8× 1×supported in directional mode) 3 2/3 10.048  — 4× —

The LRP modes are utilized in a device discovery process which involvesa station location map set-up procedure, a location information updateprocedure and a location and distance information query procedure, asdescribed below. The device location information can then be utilizedfor direct link transmission, frame preamble and payload size reductionfor unicast transmissions, and LRP preamble and payload size reductionfor multicast transmissions, as described further below.

FIG. 2 shows an example process 17 for device discovery according to thepresent invention, including the steps of: directionally transmitting adata unit over a channel in different directions from a transmittingstation in the network to emulate omni-directional transmission (step19); receiving the data unit transmissions from the different directionsat a receiving station in the network (step 21); determining the qualityand parameters of the transmissions received from the differentdirections (step 23); and determining location information for thetransmitting station relative to the receiving station based on thehighest quality received transmission among the received transmissionsreceived from the different directions (step 25). The above steps aredescribed in more detail below.

Device Discovery

Location Map Set-Up

In omni-directional emulation mode, the same information isretransmitted (repeated) in N different directions on the LRP channel bybeamforming to emulate omni-directional transmission, according to thepresent invention.

During an association stage wherein the stations are associated forcommunication, MAC frames are exchanged in omni-directional emulationmode between stations. For example, as shown in FIG. 3, in the LRP modes1 through 3, a data unit (e.g., a frame or packet) is transmitted from atransmitting station at a location 13 to N=8 different directions 15(e.g., direction sections 1, 2, . . . , 8, each covering a 45 degreeangle) to emulate omni-directional transmission. When a frame isreceived, a receiving station can measure and compare the signal quality(and other parameters) of the received frame, with that of other copiesof the frame received from the transmitting station in other directions.Then, based on such measurement and comparison, the receiving stationdetermines the direction of the transmitting station relative to thereceiving station, as location information. The direction of thetransmitting station is one of the sections 15 in FIG. 3 (or sectionboundary) along which the highest quality transmission of the frame fromthe transmitting station was measured. The receiving station maintainsthe location information for each associated station. Further, eachassociated station also maintains location information for itself andother stations identified in broadcast beacons.

For example, in an association the coordinator 12 is associated with adevice 14 for communication, wherein MAC frames are exchanged inomni-directional emulation mode between the coordinator 12 and thedevice 14. When a frame is received, the coordinator 12 or the device 14can measure and compare the signal quality (and other parameters) of theframe, with that of other copies of the frame from other directions.Then, based on such measurement and comparison, the coordinator 12 ordevice 14 determines the direction of the device 14 relative to thecoordinator 12, as location information. The direction of the device 14is along a section in FIG. 3 (or section boundary) along which thehighest receive signal level was measured. The coordinator 12 maintainsthe location information for each associated device in a device list.Further, each associated device 14 also maintains the locationinformation for itself and other devices 14 identified in broadcastbeacons.

The term “location” as used herein is an abstract concept related togeographic location, but not exactly equal to geographic location.Usually geographically proximate stations are close to each other inlocation, however, there can be exceptions due to environmental andchannel conditions. The location information can be represented as alocation map comprising a location vector. For N directionalretransmissions (i.e., Nx or N repetitions) of a data unit in a LRP modealong N corresponding directions, the location vector includes Nelements. Each element describes the signal quality or other parametersof the data transmission for one of the N directions.

Location Information Update

In one implementation, the coordinator 12 periodically transmits a dataunit comprising a beacon frame in omni-directional emulation mode,wherein N copies of the beacon frame are directionally transmitted in Ndifferent directions, as described. When receiving a beacon frame fromthe coordinator 12, a receiving device 14 measures and compares thesignal quality (and other parameters) for copies of the beacon framereceived from the coordinator 12 in different directions. The receivingdevice 14 utilizes comparison of such signal quality and parameters todetermine a new location vector for the coordinator 12. Then a“distance” between the new location vector and the existing locationvector (e.g., in a device list) is determined. The term “distance” asused herein is an abstract concept, related to geographic distance butnot exactly equal to geographic distance.

If the distance is larger than a pre-defined threshold, then the device14 attempts to send a location updating control frame to the coordinator12 within an un-reserved channel time block (FIGS. 5A-B, describedfurther below). An optional acknowledgement (ACK) can be sent back fromthe coordinator 12 to announce the successful reception of the locationupdating control frame. The coordinator 12 updates the locationinformation for the device 12 stored in its device list. Optionally, thecoordinator 12 announces the new (updated) location information for thedevice 14 in a next beacon transmission from the coordinator 12.

Location and Distance Information Query

For direct link transmission between the devices 14, a first device 14may require location information for one or more other devices in thenetwork and also the corresponding distance information. The coordinator12 maintains the location information for the devices 14 relative to thecoordinator 12. The first device 14 sends a location query requestcontrol frame for location information of one or more devices 14 to thecoordinator 12 (e.g., transmitted within an un-reserved channel timeblock). An optional ACK can be sent back from the coordinator 12 toannounce the successful reception of the location query request controlframe. The coordinator 12 then responds to the device 14 with a locationquery response command frame which provides location informationincluding distance information for one or more devices in the network.The first device then determines location information of a second devicerelative to the first device using the location information of the firstdevice relative to the coordinator and the location information of thesecond device relative to the coordinator.

An example in FIG. 4 shows a device 14 designated as Device A, anotherdevice 14 designated as Device B and the coordinator 12. Device A knowsits location vector V_(CA) in relation to the coordinator 12, and DeviceB knows its location vector V_(CB) in relation to the coordinator 12.Device A requires location information for Device B. Device A obtainsthe location information of Device B (i.e., V_(CB)), from thecoordinator 12 by location query signaling, as described. Then, Device Aestimates the distance information from Device A to Device B asV_(AB)=V_(CA)−V_(CB), where “−” is a type of vector subtractionoperation. Alternatively, the coordinator 12 can calculate V_(AB)directly and send it to Device A directly. Due to influence ofenvironmental and channel conditions, the actual distance from Device Ato Device B can be different from V_(AB). However, usually V_(AB) is agood estimate of the actual distance between Device A and Device B.

Device discovery and location detection according to the presentinvention does not require additional signaling or signaling modulesother than the coordinator 12 and devices 14 themselves. Further, usingthe location and distance information for the devices, the PHY preambleoverhead in the PHY headers, and PHY payload size are reduced. Thus, theoverall throughput of WiHD network is improved.

Channel Access Control

The coordinator 12 uses a LR channel 16 and a HR channel 18, forcommunication of video information with the devices 14. Each device 14uses the LR channel 16 for communications with other devices 14. The HRchannel 18 only supports single direction unicast transmission with,e.g., multi-Gb/s bandwidth to support uncompressed HD videotransmission. The LR channel 16 can support bi-directional transmission,e.g., with at most 40 Mbps throughput. The LR channel 16 is mainly usedto transmit control frames such as acknowledgement (ACK) frames. Somelow-rate data such as audio and compressed video can be transmitted onthe LR channel between two devices 14 directly.

The HR channel only supports single direction unicast transmission withmulti-Gb/s bandwidth to support uncompressed HD video. The LR channelcan support bi-directional transmission with at most 40 Mbps throughput.A low-rate channel is mainly used to transmit control frames such as ACKframes. It is also possible some low-rate data like audio and compressedvideo can be transmitted on the low-rate channel between two devicesdirectly.

As shown by the example timing diagram in FIG. 5, TDD scheduling isapplied to the LR and HR channels 16 and 18, whereby at any one time theLR and HR channels 16 and 18, cannot be used in parallel fortransmission. In the example of FIG. 6, beacon and ACK packets/framesare transmitted over the LR channel 16 in between transmission ofpackets of data (e.g., video, audio and control message) informationover the HR channel 18. Beamforming technology can be used in both theLR and HR channels. The LR channel can also support omni-directiontransmissions. The HR channel and the LR channel are logical channels.

In many wireless communication systems, a frame structure is used fordata transmission between wireless stations such as a transmitter and areceiver. For example, the IEEE 802.11 standard uses frame aggregationin a MAC layer and a PHY layer. In a typical transmitter, a MAC layerreceives a MAC Service Data Unit (MSDU) and attaches a MAC headerthereto, in order to construct a MAC Protocol Data Unit (MPDU). The MACheader includes information such a source addresses (SA) and adestination address (DA). The MPDU is a part of a PHY Service Data Unit(PSDU) and is transferred to a PHY layer in the transmitter to attach aPHY header (including a PHY preamble) thereto to construct a PHYProtocol Data Unit (PPDU). The PHY header includes parameters fordetermining a transmission scheme including a coding/modulation scheme.Before transmission as a packet from a transmitter to a receiver, apreamble is attached to the PPDU, wherein the preamble can includechannel estimation and synchronization information.

There are two approaches for a wireless station (STA) to access a sharedwireless communication channel. One approach is a contention-freearbitration (CF) method, and the other is a contention based arbitration(CB) method. There are multiple channel access methods for a CF period.For example, a point coordinator function (PCF) can be utilized tocontrol access to the channel. When a PCF is established, the PCF pollsregistered STAs for communications and provides channel access to theSTAs based upon polling results. The CB access method utilizes a randomback-off period to provide fairness in accessing the channel. In the CBperiod, a STA monitors the channel, and if the channel has been silentfor a pre-defined period of time, the STA waits a certain period oftime, such that if the channel remains silent, the STA transmits on thechannel.

The coordinator and the non-coordinator devices share the samebandwidth, wherein the coordinator coordinates the sharing of thatbandwidth. Standards have been developed to establish protocols forsharing bandwidth in a wireless personal area network (WPAN) setting. Asnoted, the IEEE standard 802.15.3 provides a specification for the PHYlayer and the MAC layer in such a setting where bandwidth is sharedusing a form of time division multiple access (TDMA). According to thepresent invention, the MAC layer defines a superframe structure,described below, through which the sharing of the bandwidth by thenon-coordinator devices 14 is managed by the coordinator 12 and/or thenon-coordinator devices 14.

According to the present invention, in a contention-free period, insteadof PCF polls, time scheduling is utilized wherein beacons provideinformation about scheduled channel time blocks for devices. Asuperframe-based channel access control for transmission of uncompressedvideo over wireless channels, according to the present invention, isapplied based on a superframe structure shown by example in FIGS. 6A-B.FIG. 6A shows a sequence of superframes 20, and FIG. 6B shows thedetails of a superframe 20 for the LR and HR channels including multipleschedules 30. Each schedule 30 includes one or more periodical reservedchannel time blocks (CTBs) 32 which are reserved for transmission ofisochronous data streams. Each schedule 30 includes multiple reservedCTBs 32, wherein duration of a schedule is divided between multiple CTBs32. Each reserved CTB 32 is allocated to a portion of the correspondingschedule, wherein T1 indicates the time period between the start of eachSchedule1 interval, and T2 indicates the time period between the startof each Schedule2 interval.

The schedules 30 represent reserved CTBs 32, and the time periodsbetween the schedules 30 are unreserved CTBs. As such, each superframe20 includes two CTB categories: reserved CTBs 32 and unreserved CTBs 37.Such a superframe 20 is useful for channel access control using CTBs fortransmission of uncompressed video over wireless channels (e.g., the HRchannel 18 and the LR channel 16). Beacons are used to separate channeltime into multiple superframes. In each superframe there are contentionperiods and contention-free periods. In each CFP there are one or moreschedules. A superframe includes a contention-based control period(CBCP), a CFP including multiple reserved channel time blocks (RCTBs)and/or unreserved channel time blocks (UCTBs). Specifically, thesuperframe 20 includes:

-   -   1. A beacon frame (“beacon”) 22 which is used to set timing        allocations and to communicate management information for the        network 10 (e.g., WiHD sub-net). It is assumed that beacon        signals are always transmitted omni-directionally.    -   2. A CBCP 24 is used to communicate Consumer Electronic Commands        (CECs) and MAC control and management commands on the LR channel        16. No information can be transmitted on the HR channel 18        within the CBCP period. There can also be a beam-search period        (BSP) between the CBCP 24 and the CFP 28 to search transmission        beams and to adjust beamforming parameters (e.g., every 1˜2        seconds a BSP can appear in the corresponding superframe 20).    -   3. The CFP 28 which includes said CTBs comprising one or more        reserved CTBs 32 and one or more unreserved CTBs 37.

The reserved CTBs 32 are reserved by one or multiple devices 14 fortransmission of commands, isochronous streams and asynchronous dataconnections. The reserved CTBs 32 are used to transmit commands,isochronous streams and asynchronous data connections. Each reserved CTB32 can be used for transmitting a single data frame or multiple dataframes. The schedules 30 organize the reserved CTBs 32. In eachsuperframe 20, a schedule 30 can have one reserved CTB 32 (e.g., forpre-scheduled beam-searching or bandwidth reservation signaling) ormultiple periodical reserved CTBs 32 (e.g., for an isochronous stream).Unreserved CTBs 37 are typically used to transmit CECs (and MAC controland management commands on the LR channel. No beamforming transmissionis allowed within the unreserved CTBs. Unreserved CTBs 37 can also beused for transmission of control and management packets between devices14 if direct link support (DLS) is allowed. During an unreserved CTB 37,only the LR channel, operating in an omni-direction mode, can beutilized. No information can be transmitted on the HR channel during anunreserved CTB 37. Different contention-based medium access mechanisms,such as a carrier sense multiple access (CSMA) scheme or a slotted Alohascheme can be used during an unreserved CTB 37.

A beacon 22 is transmitted periodically to identify the start of everysuperframe 20. Configuration of the superframe 20 and other parametersare included in the beacon 22. For example, the beacon 22 indicates thestart time and length of the periods CBCP 24 and the CFP 28. Inaddition, the beacon 22 dictates allocation of the CTBs in the CFP 28 todifferent devices 14 and streams. Since devices can implicitly know thetiming information of unreserved CTBs, a beacon frame need not carrytiming information for unreserved CTBs.

For reservation-based time allocation, data transmissions usingbeamforming must be reserved in advance. A device 14 requestssend-bandwidth from the coordinator 12 for the transmission of bothisochronous streams and asynchronous data. If there is enough bandwidth,the coordinator 12 allocates a schedule for the requesting device. Eachschedule includes a series of evenly distributed reserved CTBs 32 havingequal durations. A schedule can include multiple reserved CTBs 32, orone reserved CTB 32 in a superframe 20, or one reserved CTB 32 in everyN superframes 20. Usually an isochronous stream is transmitted withinone schedule for each superframe 20. However, it is also possible toallocate multiple schedules for one isochronous or asynchronous stream.Multiple streams belonging to the same device can also be transmittedwithin one schedule. Each data packet 31 transmitted from a device to adestination has a corresponding ACK packet 33 sent back from thatdestination, wherein each data packet 31 and corresponding ACK packet 33form a data-ACK pair. A CTB 32 can include a single data-ACK pair ormultiple data-ACK pairs.

A schedule can be reserved for periodic beam-searching in which onereserved CTB 32 appears every 1˜2 seconds. Periodic beam-searching canalso be performed within unreserved CTBs. In addition to periodicbeam-searching, event-driven beam-searching (i.e., dynamicbeam-searching) can be triggered by factors such as bad channel status.If event-driven beam-searching is to be implemented without affectingother reserved schedules, the length of any reserved CTB for a schedule(T_(reserved) _(—) _(CTB)) plus the length of unreserved CTBsimmediately after the reserved CTB (T_(un) _(—) _(reserved) _(—) _(CTB))should not be less than the length of a beam-searching periodT_(beam-searching) (e.g., 400 μs as default). As such, T_(reserved) _(—)_(CTB)+T_(un) _(—) _(reserved) _(—) _(CTB)≧T_(beam-searching).

Utilization of Device Location Information for Communication Using aSuperframe

As noted, the device location information can be utilized for directlink transmission, frame preamble and payload size reduction for unicasttransmissions, and LRP preamble and payload size reduction for multicasttransmissions, as described below.

Direct Link Transmission

A device 14 in the WVAN can communicate with another device 14 usingdirect link transmission, according to the present invention. During adirect link set-up stage, the two devices 14 conduct a probing messageexchange using a LRP mode omni-direction transmission to ensure that thetwo devices 14 can receive signals from each other successfully. After asuccessful probing, indicating that the two devices 14 can receivesignals from each other successfully, a link assessment/recommendationor beam-searching/steering process can be conducted to obtain accuratecommunication link status information, and to set propertransmission/receiving configurations for the two devices.

FIG. 7 shows an example management entity (ME) 40 for implementing suchdirect link transmission, wherein the ME 40 includes a MAC layermanagement entity (MLME) function 48 for managing MAC layer operationsand a device management entity (DME) function 46 for establishing achannel and controlling channel access. The DME function 46 and the MLMEfunction 48 can be implemented in the same device or on differencedevices. Further, the coordinator 12 and each of the devices 14 caninclude a ME 40. The ME 40 further provides monitoring and controlfunctions to a MAC layer 42 and a PHY layer 44, and facilitatescommunication between the upper layers 45 and the MAC layer 42. The MLMEmessages below are defined by the IEEE 802.15.3 standard (“WirelessMedium Access Control (MAC) and Physical Layer (PHY) Specifications forHigh Rate Wireless Personal Areas Networks (WPANs),” 2003). Theoperations of the DME and MLME functions in response to the MLMEmessages are according to the present invention, as described below byexample in relation to FIG. 8.

FIG. 8 shows an example process 50 for direct link communication betweentwo devices 14 such as a device n (Dev-n) and a device m (Dev-m). Whenthe Dev-n desires to set-up a direct link transmission with the Dev-m,in step 52 the Dev-n sends a bandwidth reservation request command(indicating the amount of bandwidth requested) to the coordinator 12within an unreserved CTB. In step 54 the coordinator 12 checks theavailable channel bandwidth and also the availability of the Dev-m, andin step 56 the coordinator 12 sends back a bandwidth response command tothe Dev-n. Specifically, in step 56 if the available bandwidth issufficient to satisfy the request, and the Dev-m is available, thecoordinator 12 reserves CTBs for the requested bandwidth and responds tothe Dev-n with a bandwidth response command that grants the bandwidthreservation request; otherwise, the coordinator 12 responds with abandwidth response command that rejects the bandwidth reservationrequest.

After obtaining the reserved bandwidth, during a reserved CTB for directlink transmission, in step 58 the Dev-n probes the Dev-m by sending adirect link transmission (DLT) probe request command frame as a MACcommand in omni-directional emulation mode in a LRP, and waits for a DLTprobe response from the Dev-m. Upon successful reception of the DLTprobe request frame, in step 60 the Dev-m measures and compares thesignal quality and other parameters of repetition copies of the DLTprobe request frame received in different directions from the Dev-n, anddetermines the direction of the Dev-n relative to Dev-m. Then, in step62 the Dev-m sends back a DLT probe response command with channelcoefficients information to the Dev-n. If the Dev-n cannot obtain a DLTprobe response command after a waiting period (e.g., mDLTProbeWaitTime),the Dev-n may then repeatedly send the DLT probe request command anumber of times (e.g., mMaxDLTProbing times).

Upon receiving a DLT probe response command from the Dev-m, a DLT proberequest/response exchange may be repeated between the Dev-n and Dev-m upto a threshold (e.g., mMaxDLTProbingNum times). After the probingprocedure, if probing of the Dev-m by the Dev-n in omni-directional modeat the LRP is successful, then in step 64, the MAC layer of the Dev-nreports a successful DLT set-up to the DME with a MLME-DLS.cfm primitivemessage; otherwise, the Dev-n sends a bandwidth request command to thecoordinator 12 to release the reserved CTBs and reports a DLT set-upfailure to the DME with a MLME-DLS.cfm primitive message in step 64.

Then in step 66, a link assessment/recommendation orbeam-searching/steering in directional mode at the HRP or LRP may beconducted to obtain accurate link status information in directional modeand set proper transmission/reception configurations before startingtransmission of audio/video or data streams over the channels. Then, instep 68, communication of audio/video/data streams in the reserved CTBsbetween the Dev-n and Dev-m commences.

LRP Preamble and Payload Size Reduction for Unicast Transmission

A device 14 knows its location relative to the coordinator 12 byreceiving beacons periodically transmitted from the coordinator 12.Based on such location information, the device 14 only needs to send aPHY preamble and PHY payload at the directions with good signal quality.Thus the device 14 can reduce the size of the PHY preamble and payloadin the MAC frames it transmits to the coordinator 12. Specifically, thedevice 14 can reduce the size of the PHY preamble and PHY payload fromN-times (i.e., Nx) to M-times (i.e., Mx) wherein N≧M, according to thelocation vector of device 14 and without requiring accuratebeam-searching, provided that all devices 14 are within M directionsections (FIG. 3) of the coordinator 12. Similarly, if the coordinator12 only wants to transmit a MAC frame to one device 14, the coordinator12 can reduce the size of the PHY preamble and the payload in the MACframes it transmits to the device 14 from Nx to Mx (wherein N≧M)according to the location vector of the coordinator 12, withoutrequiring accurate beam-searching since the coordinator 12 can obtainlocation updates from the device 14.

LRP Preamble and Payload Size Reduction for Omni-Direction MulticastTransmission

When the coordinator 12 is a multicast source in a multicast group,since the coordinator 12 knows the locations of all destination devices14 in the multicast group, the coordinator 12 can reduce the PHYpreamble and payload size in its multicast MAC frames from Nx to Mx(N≧M), provided that all destination devices 14 are within M directionsections (FIG. 3) of the coordinator 12.

When a device 14 is a multicast source in a multicast group, the device14 can obtain the locations of all devices in the multicast group usinglocation query exchanges, and then calculate the location vectors of allother devices in relation to the multicast source. Then, the device 14can reduce the size of the PHY preamble and payload in its multicast MACframes from Nx to Mx (N≧M), provided all destination devices are withinM direction sections (FIG. 3) of the multicast source device 14.

As is known to those skilled in the art, the aforementioned examplearchitectures described above, according to the present invention, canbe implemented in many ways, such as program instructions for executionby a processor, as logic circuits, as an application specific integratedcircuit, as firmware, etc.

The present invention has been described in considerable detail withreference to certain preferred versions thereof; however, other versionsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the preferred versionscontained herein.

1. A method for device discovery in a wireless network, comprising:directionally transmitting a data unit from a transmitting station overa channel in different directions to emulate omni-directionaltransmission; receiving the data unit transmissions from differentdirections at a receiving station; determining the quality of thetransmissions received from the different directions; detecting locationinformation for the transmitting station relative to the receivingstation based on the highest quality transmission among thetransmissions received from the different directions, wherein thelocation information comprises a location vector including N elementscorresponding to directional transmissions of a data unit in N differentdirections, wherein each vector element describes the signal quality ofthe transmission along a corresponding one of the N directions; acoordinator station transmitting a beacon, wherein N copies of thebeacon are directionally transmitted in N different directions; thereceiving station measuring and comparing the signal quality for copiesof the beacon received from the coordinator station in differentdirections, to determine a new location vector for the coordinatorstation; the coordinator station periodically transmitting the beacon inomni-directional emulation mode; and determining a distance between thenew location vector and an existing location vector.
 2. The method ofclaim 1 wherein detecting location information further includesdetermining the direction of the transmitting station relative to thereceiving station, as location information.
 3. The method of claim 1wherein said channel comprises a low rate channel implementingorthogonal frequency division multiplexing (OFDM), providing bothomni-directional and beam-steered modes.
 4. The method of claim 3wherein directionally transmitting comprises transmitting a data unit indifferent directions by beam-steering transmission of the data unit insaid different directions.
 5. The method of claim 3 wherein transmissiondata rates for the channel range from 2.5 Mb/s to 10 Mb/s for theomni-directional mode, and 20 Mb/s to 40 Mb/s for the beam-steered mode.6. The method of claim 3 wherein the channel is in the 57.2 GHz to 65.8GHz frequency band.
 7. The method of claim 1 wherein the data unitcomprises a frame.
 8. The method of claim 1 further comprising: thereceiving station maintaining location information for the locationinformation for each associated station.
 9. The method of claim 8further comprising: each associated station maintaining locationinformation for itself and other stations identified in beaconsbroadcast by the coordinator station.
 10. The method of claim 1 furthercomprising: if the distance is larger than a pre-defined threshold, thenthe receiving station transmitting a location updating control frame tothe coordinator station; and the coordinator station updating thelocation information for the receiving station maintained by thecoordinator.
 11. The method of claim 10 further comprising: thecoordinator announcing the new location information for the receivingstation in a next beacon transmission from the coordinator station. 12.The method of claim 1 further comprising: a coordinator stationmaintaining location information for associated stations in the networkrelative to the coordinator; a first associated station sending alocation query request control frame to the coordinator station forlocation information of one or more other associated stations; thecoordinator station providing location information of said one or moreother associated stations to the first associated station; and the firstassociated station determining location information of a second devicerelative to the first associated device using: the location informationof the first associated device relative to the coordinator station, andthe location information of the second associated device relative to thecoordinator station.
 13. The method of claim 1 further comprising: thecoordinator station maintaining location information for associatedstations in the network relative to the coordinator station; thecoordinator station periodically transmitting said location informationin a beacon; and an associated receiving station using a reduced PHYpreamble and reduced payload in a frame transmission to the coordinatorstation based on the corresponding location information.
 14. The methodof claim 13 further comprising: a coordinator station maintaininglocation information for associated stations in the network relative tothe coordinator station; a multicast source station in a multicast groupobtaining location information of stations in the multicast group byperforming location query exchanges with the coordinator station;determining the location information of other stations in relation tothe multicast source; and the multicast source using a reduced PHYpreamble and payload in a frame transmission to the coordinator stationbased on the corresponding location information.
 15. The method of claim1, wherein the coordinator station comprises a sink of one of videodata, audio data, and video and audio data.
 16. The method of claim 1,wherein the coordinator station provides channel coordination functionsfor wireless communication between a sink station and a source station.17. The method of claim 1, wherein the coordinator station uses a highrate channel and a low rate channel for communicating video informationwith the receiving station and transmitting station, wherein the highrate channel only supports single direction unicast transmission forsupport of uncompressed high definition (HD) video data, and the lowrate channel supports bi-directional transmission.
 18. A system fordevice discovery in a wireless network, comprising: a communicationmodule configured for directionally transmitting a data unit from atransmitting station over a channel in different directions to emulateomni-directional transmission; a management entity configured forreceiving the data unit transmissions from different directions at areceiving station, a coordinator station configured for N copies of abeacon in N different directions; wherein the management entity isfurther configured for measuring and comparing the signal quality forcopies of the beacon received from the coordinator station in differentdirections, to determine a new location vector for the coordinatorstation, wherein the coordinator station is further configured forperiodically transmitting a beacon in omni-directional emulation mode,and for-determining a distance between the new location vector and anexisting location vector; determining the quality of the transmissionsreceived from the different directions, and detecting locationinformation for the transmitting station relative to the receivingstation based on the highest quality transmission among thetransmissions received from the different directions, wherein thelocation information comprises a location vector including N elementscorresponding to directional transmissions of a data unit in N differentdirections, wherein each vector element describes the signal quality ofthe transmission along a corresponding one of the N directions.
 19. Thesystem of claim 18 wherein the management entity is further configuredfor detecting location information by determining the direction of thetransmitting station relative to the receiving station, as locationinformation.
 20. The system of claim 18 wherein said channel comprises alow-rate channel implementing orthogonal frequency division multiplexing(OFDM), providing both omni-directional and beam-steered modes.
 21. Thesystem of claim 20 wherein the communication module is furtherconfigured for directionally transmitting a data unit in differentdirections by beam-steering transmission of the data unit in saiddifferent directions.
 22. The system of claim 20 wherein transmissiondata rates for the channel range from 2.5 Mb/s to 10 Mb/s for theomni-directional mode, and 20 Mb/s to 40 Mb/s for the beam-steered mode.23. The system of claim 20 wherein the channel is in the 57.2 GHz to65.8 GHz frequency band.
 24. The system of claim 18 wherein the dataunit comprises a frame.
 25. The system of claim 18 wherein the receivingstation maintains location information for the location information foreach associated station.
 26. The system of claim 16 wherein thecommunication module comprises another management entity configured fordirectionally transmitting a data unit from a transmitting station overa channel in different directions to emulate omni-directionaltransmission.
 27. The system of claim 26 wherein: the receiving stationis configured such that, if the difference between new locationinformation and the previous measured location information is largerthan a pre-defined threshold, then the receiving station transmits alocation updating control frame to the coordinator station; and thecoordinator station is further configured to updating the locationinformation for the receiving station maintained by the coordinatorstation.
 28. The system of claim 27 wherein the coordinator station isfurther configured for announcing the new location information for thereceiving station in a next beacon transmission from the coordinatorstation.
 29. The system of claim 16 further comprising: the coordinatorstation configured for maintaining location information for associatedstations in the network relative to the coordinator station; a firstassociated station configured for sending a location query requestcontrol frame to the coordinator station for location information of oneor more other associated stations; wherein the coordinator station isfurther configured for providing location information of said one ormore other associated stations to the first associated station; and thefirst associated station is further configured for determining locationinformation of a second device relative to the first associated deviceusing: the location information of the first associated device relativeto the coordinator station, and the location information of the secondassociated device relative to the coordinator station.
 30. The system ofclaim 16 further comprising: a coordinator station configured formaintaining location information for associated stations in the networkrelative to the coordinator station; the coordinator station furtherconfigured for periodically transmitting said location information in abeacon; and an associated receiving station configured for using areduced PHY preamble and reduced payload in a frame transmission to thecoordinator station based on the corresponding location information. 31.The system of claim 30 wherein: the coordinator station is furtherconfigured for maintaining location information for associated stationsin the network relative to the coordinator station; the system furthercomprising a multicast source station in a multicast group configuredfor obtaining location information of stations in the multicast group byperforming location query exchanges with the coordinator station,determining the location information of other stations in relation tothe multicast source, and using a reduced PHY preamble and payload in aframe transmission to the coordinator station based on the correspondinglocation information.
 32. A method for device discovery in a wirelessnetwork, comprising: directionally transmitting a data unit from atransmitting station over a channel in different directions to emulateomni-directional transmission; receiving the data unit transmissionsfrom different directions at a receiving station; determining thequality of the transmissions received from the different directions;detecting location information for the transmitting station relative tothe receiving station based on the highest quality transmission amongthe transmissions received from the different directions, wherein thelocation information comprises a location vector including N elementscorresponding to directional retransmissions of a data unit in Ndifferent directions, wherein each vector element describes the signalquality of received directional retransmission along a corresponding oneof the N directions; a coordinator station transmitting a beacon,wherein N copies of the beacon are directionally transmitted in Ndifferent directions; and a receiving station measuring and comparingthe signal quality for copies of the beacon received from thecoordinator station in different directions, to determine a new locationvector for the coordinator station.